RTC deviation definition for C-IoT Intel products

Purpose:

It lists C-IOT Intel product's RTC deviation for customer reference, 

Target Audience:

For Advantech TSE, RBU AE, outsourcing service engineer(s) and End customer with the following knowledges  :

• Hardware troubleshooting experience

Content:

Almost C-IoT Intel products are using PCH RTC, the RTC deviation definition needing to following Intel PCH RTC specification.

Following link is Intel RTC definition, and Intel specifies an RTC deviation of 1.728 seconds per day when the CMOS battery is in normal power status

Intel® I/O Controller Hub (Intel® ICH) / Platform Controller Hub (PCH) Family Real Time Clock (RTC):

https://www.intel.com/content/dam/www/public/us/en/documents/application-notes/ich-family-real-time-clock-accuracy-considerations-note.pdf

Chapter 3.3.1 (P15)

The RTC accuracy can be affected by the voltage of battery. In general, when the battery voltage decays, the RTC accuracy also decreases. High accuracy (less than ±10 ppm which does not include Crystal’s tolerance) can be obtained when VccRTC is larger than the min voltage specification.

For example: 20 ppm is equivalent with 1.728 sec error in one day.PPM = ((Fo – 32.7680) / 32.768) * 10^61 day = 24 hours/day * 60 min/hour * 60 sec/min = 86400 sec20 ppm * 1 day (86400 sec) = (20 * 86400) / 1000000 = 1.728 sec